My understanding is humans have a limited capacity for glucose storage--
"350 g as muscle glycogen, 90 g in the liver and a small amount of circulating glucose in the blood" [http://www.healthline.com/hlbook/nut-carbohydrate-metabolism]
Anything additional is changed into fat.
It's not that simple. I think you missed my point. Either way I still am not satisfied. You see, even if your quote would be accurate, it would still mean you might need to consume more than 400g of carbs a day. Which is mad if you're trying it with bananas and vegetables. Like I said, almost all fruits and veggies are 80% or more water, which leaves them to mere 5-20g of carbs/100g. When in oats or similar grain has over 50g of carbs per 100g.
Still, my point was that there are exceptions. First off, people are different. There is no exact amount of glycogen body can store. No, it's more logical than that. Muscles store glycogen. The more muscle you have, the more glycogen you can store. Peoples resting glucogen in muscle can also vary alot. non-athletes have something like 120mmol/kg. Elite athletes can have muscle glucogen levels up to 200mmol/kg. The science behind all this isn't just as simple as that. There is no exact limit of carbs that is the same for every person. Even if you are eating over your storaging amount, it doesn't mean you will build fat instantly. No, Exercising changes everything. Carbs can be taken before exercising (loading phase or performance enhancing in general), during exercises (almost necessary with long and hardcore sports), or afterwards. Some sources even say athletes can take over 1000g of carbs per day and not get over 10% bodyfat any time of the year. The more training hours you have combined with the intensity of the exercise, the more carbs you should eat. I'm talking about extremes here, but for an example, doing high-intensity exercises like cycling or running for 4-5 hours a day can burn over 900g's worth of carbohydrates. Now I admit that there's no storage in muscle that can store that kind of amount of carbs. But suprise, you don't have to storage that kind of amount.
You can infact increase your glycogen storages by a loading phase before an exercise, but it's all about what happens afterwards. You have to have a little depletion to not build that fat from the carbs. The depletion will stimulate an enzyme called glycogen synthase. Glycogen synthase is the thing responsible for excessive carbo storaging. Also after your exercises, glycogen synthesis is very rapid after exercising, and the fastest phase can last for over 2 hours. Then there's some slower rate synthesis for over 24 hours. So body needs way more glycogen than you got in your storages. And that's one of the reasons you eat carbs to recover. And that amount is in most cases a bit larger. Some sources even recommend 225g of carbs within the couple of hours after exercising, then more later. And I wasn't even mentioning the methods to weight and muscle gains. Carbs are one important source of nutrition if you want bigger muscles. It kinda relates to all that science above.
This is a bit of unaverage person or an elite level example, but I still would like to hear if paleo has solution for this kind of exercising. Maltodextrin and pure glucose/fructose?
Since humans have an unlimited capacity to store fat and not carbs, protein or alcohol; I believe fat is our bodies preferred fuel source.
Grains are really just calorie supplements; If you can't get enough calories, supplement with the less nutritious grain products.
It's not that simple. It would be easy if fat burning would just happen every time we need energy, but no. It doesn't work that way. Fat oxidation only occurs with low intensity, or after an intensive workout. When you are going higher on intensity level, especially if you're doing it for a longer period of time, using only fat storages will kill your performance level. You need ATP, the primary fuel for exercising. You get it from carbs, fats and when necessary, protein. But there are differences. First off, body can form ATP from carbs almost twice as fast than from fats. Secondly, when in anaerobic or intensive exercise, you can make five times then energy from carbs than you get from fats. So performance wise, it's not all about fats. It takes high conditioning and practise to burn fat efficiently during an exercise. If you are in a long exercise, you will notice when the body starts using fats instead of carbs. It's like a minor wall hitting your muscles.
I think carbs are the fuel for exercising, fats for other living and rest. For an elite athlete I would never recommend losing carbs before an event or after it. It just makes no sense. It's not just "additional calories". Calories don't matter at all. It's all about the need of protein, carbs and fats. But excess carbs and not enough exercise to match it will get you fat and sick, that's a given. And for that I totally understand the no-grain diets and paleo. Once again, I'm just wondering if there is something I don't know or think at this moment. Something that would solve my puzzle.